Dynamo-electric machine.



M. WALKER. DYNAMO ELECTRIC MACHINE.

APPLICATION FILED MAY 16. 19%0.

1,156,645. Patented 001;. 12, 1915.

WITNESSES: NV NTOR (a NM ATTORNEY coLiJMBIA PLANOGRAPH CO..WA5H[NGTDN. Dc.

UNITED STA BTES PATENT OFFICE.

MILES WALKER, OF HALE, ENGL ND, ASSIGNQR TO UTESTII'IGHQUSE ELECTRIC ANDMANUFACTURING CQM DYN To all whom it may concern:

'Be it known that I, MlLns WALKER, a subject of the King of GreatBritain, and a resident of Hale, in the county of Chester, England, haveinvented a new and useful Improvement in Dynamo-Electric Machines, ofwhich the following is a specification.

My invention relates to dynamo electric machines and particularly torotary converters and motor generators, and it has for its object toprovide a machine of'this character-in which the voltage generated atthe direct current brushes of the machine may be varied while thevoltage on its alternating current side remains constant.

It is well known that, if the direct current brushes of a rotaryconverter or motorgenerator are rocked either forward or backward I fromthe neutral position, the voltage across them is decreased, but, inmachines, as commonly constructed, it is not possible to vary the directcurrent voltage in this manner through a very wide range becausemovement of the brushes a considerable distance from the neutralposition produces serious sparking.

According to my present invention, the strength of the magnetic fieldunder the poles or parts of the poles, and the length and resistance ofthe conductors connecting two adjacent commutator bars are soproportioned that it is possible to rock the brushes over a wide arewithout causing sparking. I am, therefore, able to obtain a Widevariation of voltage on the direct current side of the machine byrocking the brushes forward or backward.

For the purpose of explanation, the pole arc may be regarded as dividedinto two parts and a region under each pole which is spanned by thefirst part of the pole arc, when taken in the direction of rotation,will be considered. This region of the pole face has ordinarily amagnetic flux passing through it of such polarity as to generate, in theconductors moving under it, an electromotive force whichis in the rightdirection to commutate the current generated in the armature. If theabove mentioned netic flux has its proper value, conductors connected tothe commutator bars upon which the brushes rest when rocked into theirforward position will have generated therein an electro-motive forcewhich is of the proper value to produce perfect com- Specification ofLetters Patent.

3-3, A COBEORATIGN OF PENNSYLVANIA.

.O-ELECTRIC 'MACEINE.

Serial N0. 561,749.

mutation. If narrow carbon brushes are used or if resistances areinserted into the circuits which would ordinarily be shortcircuited bythe brushes, it is possible to have quite a large variation in thestrength of the above mentioned flux and yet obtain fairly goodcommutation. Moreover, it is possible to have the fiuX of the rightstrength to produce good commutation at full load and yet to have theelectro-motive force produced in the short-circuited conductors not sogreat as to produce sparking at no load.

According to my present invention, the length of the air-gap in thefirst part, or leading pole tip of the above mentioned pole arc, and thenumber of ampere turns magnetizing it are so arranged as to produce theright strength of field to bring about these conditions, while thelength of the airgap of the remainder of the pole a "c and the number ofampere turns upon it are ar ranged to meet other conditions in thedesign.

In order that the invention may be clearly understood, a practicalembodiment of the same is illustrated in the single figure of theaccompanying drawing, which is a view, in end elevation, of a portion ofthe field magnet and armature of a rotary converter.

deferring now to the drawing, the field magnet pole pieces of a rotaryconverter or motor-generator are indicated at 1 and the armature core at2, the former being provided with a shunt field winding 3 and a seriesfield winding l, and the latter being provided with the usual slots 5for the reception of the armature coils, the conductors of one of whichare indicated at 6. The teriiinals of the conductors 6 are connected tothe segments 7 and 8, respectively, of the commutator cylinder 9 whichare shown in cont-act with one of the brushes 12 of the machine.

The face of each pole piece 1 is divided into two portions 10 and 11,the former of whichreferrcd to hereinafter as the first or leadingportion, that is to say, the porti on under which each armatureconductor first passes during its rotation-is cut away so that the airgap between said portion and the arr .ture core 2 is much greater thanthe air gtp between the second or remaining port on of the pole face andthe armature core.

Patented Oct. 12, 1915. i

It will be evident that the magnetic rcluctance of the air gap, takenover any area extending the full active length of the arma ture, thatis, the full length of the pole in a direction parallel with the axis ofthe armature and measuring one centimeter along the periphery, will bemuch greater under the first or leading portion 10 of the pole than themagnetic reluctance of the air gap measured over any like area under thesecond portion 11 of the pole. The ma g netic reluctance of the areasmeasured in this way will, however, be substantially uniform under eachportion of the pole. The effect of this arrangement is that theelectromotive force genera ted in the armature conductorsmoving underthe leading portion of the pole will not be sufficient to cause sparkingwhen these conductors are shortcircuited by brushes touching adjacentcommutator segments. The brushes may therefore be rocked to any positionwithin limits corresponding to the extent of the first portion of thepole while, at the same time, the magnetic flux through the secondportion of the pole may be made as great as is necessary to secure therequired output from the machine. It is clear, therefore, that a widerange of direct current voltage, corresponding to the above-mentionedpossible extent of displacement of the brushes, may thus be obtainedwhile maintaining good commutating conditions. For example, if it isrequired to ob tain a variation in the direct current voltage amountingto 20% of the mean voltage of the machine, the relative reluctance ofthe air gaps under the portions 10 and 11 of each pole is so designedthat the flux passing through the portion 10 of the pole is 10% of theflux passing through the portion 11. The total flux through the wholepole face is thus equal to 110% of that required to generate the meanelectromotive force at the brushes, so that, when the brushes aretouching conductors on the true neutral axis, indicated in dotted linesmidway between the axes of adjacent poles, a voltage at the brushes isobtained which is 10% higher than the mean voltage. By rocking thebrushes forward in the direction of rotation of the armature from theneutral axis, so that the flux through the portion 10 of one pole facegenerates an electro-motive force opposed to that produced by the fluxthrough the portion 11 of the adjacent pole face, a voltage at thebrushes is obtained which is 10% less than the mean voltage.

So far as the operation of the machine from the alternating current sideis concerned, very little, if any, change is made by the above describeddisplacement of the brushes, since the total flux through the whole poleremains unaltered by such displacement. It is, therefore, possible tochange the voltage on the direct current side throughout a wide rangeand yet maintain the power factor on the alternating current side at anydesired value.

I find it prefer able to employ narrow carbon brushes of high resistanceor to insert resistances into the leads which connect the armaturewinding to the commutator segments in order to reduce the currentflowing in the portions of the armature winding which are momentarilyshort circuited when the commutator segments connected thereto are underthe said brushes.

The invention may evidently be applied to any direct current machine,and, by having two or more sets of brushes, a corresponding number ofdifferent voltages may be obtained from the same machine. These andother variations of the constructional forms of the invention hereindescribed and illustrated may evidently be made without exceeding thescope thereof. If the machine is run as a direct current motor or as arotary converter from direct current to alternating current the arrowindicating the direction of rotation in the drawing will be reversed.

I claim as my invention:

1. In a direct current or double current dynamo electric generator, thecombination with an armature, a commutator cylinder to which thearmature coils are connected, and a set of adjustable brushes, of afield magnet, the polar projections of which are divided in a lineparallel to the axis of the armature into two unequal well definedportions to provide a greater air gap under the smaller portion locatedunder the leading pole tip than under the remaining larger portion ofthe pole face.

2. In a dynamo-electric machine, the combination with an armature, acommutator cylinder to which the armature coils are connected, and anadjustable set of brushes, of field magnet the polar projections ofwhich are divided in a line substantially parallel to the axis of thearmature into two well defined portions having air-gaps of differentlengths, the portion having the longer airgap being disposed on the sideof the polar projection approached by the armature when the machine isoperated as a generator.

8. In a dynamoelectric machine, the combination with an armature, acommutator cylinder to which the armature coils are connected, and anadjustable set of brushes, of a field magnet having a plurality of olarprojections severally provided with we defined zones of different fiuxdensities, the zone of the lower density being disposed under theleading pole tip when the machine is operated as a generator.

4-. In a dynamo-electric machine, the combination with an armature, acommutator cylinder to which the armature coils are connected, and anadjustable set of brushes, of

brushes cooperating with the commutator cylinder and adapted foradjustment Within said zones of Weak flux density, whereby thedirect-current voltage may be varied.

In testimony whereof, I have hereunto subscribed my name thistwenty-eighth day of April 1910.

MILES WALKER.

i/Vitnesses:

A. G. SKELTON, J. C. BoUTFLoWEB.

Copies of this patent may be obtained for five cents each, by addressingthe Commissioner of Patents Washington, I). C.

